EP0315469B1 - Vorrichtung und Verfahren zur spanabhebenden Bearbeitung - Google Patents

Vorrichtung und Verfahren zur spanabhebenden Bearbeitung Download PDF

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Publication number
EP0315469B1
EP0315469B1 EP88310398A EP88310398A EP0315469B1 EP 0315469 B1 EP0315469 B1 EP 0315469B1 EP 88310398 A EP88310398 A EP 88310398A EP 88310398 A EP88310398 A EP 88310398A EP 0315469 B1 EP0315469 B1 EP 0315469B1
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EP
European Patent Office
Prior art keywords
machining
tool
workpiece
spindle
currents
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
EP88310398A
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English (en)
French (fr)
Other versions
EP0315469A2 (de
EP0315469A3 (en
Inventor
Shigenori Ando
Ryuji Iijima
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Seiko Seiki KK
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Seiko Seiki KK
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Publication date
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Publication of EP0315469A2 publication Critical patent/EP0315469A2/de
Publication of EP0315469A3 publication Critical patent/EP0315469A3/en
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Publication of EP0315469B1 publication Critical patent/EP0315469B1/de
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C32/00—Bearings not otherwise provided for
    • F16C32/04—Bearings not otherwise provided for using magnetic or electric supporting means
    • F16C32/0406—Magnetic bearings
    • F16C32/044—Active magnetic bearings
    • F16C32/0474—Active magnetic bearings for rotary movement
    • F16C32/0489—Active magnetic bearings for rotary movement with active support of five degrees of freedom, e.g. two radial magnetic bearings combined with an axial bearing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
    • B23Q5/00—Driving or feeding mechanisms; Control arrangements therefor
    • B23Q5/02—Driving main working members
    • B23Q5/04—Driving main working members rotary shafts, e.g. working-spindles
    • B23Q5/06—Driving main working members rotary shafts, e.g. working-spindles driven essentially by fluid pressure or pneumatic power
    • B23Q5/08—Driving main working members rotary shafts, e.g. working-spindles driven essentially by fluid pressure or pneumatic power electrically controlled
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
    • B23Q1/00—Members which are comprised in the general build-up of a form of machine, particularly relatively large fixed members
    • B23Q1/70—Stationary or movable members for carrying working-spindles for attachment of tools or work
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B41/00—Component parts such as frames, beds, carriages, headstocks
    • B24B41/04—Headstocks; Working-spindles; Features relating thereto
    • B24B41/044—Grinding spindles with magnetic or electromagnetic bearings; Features related thereto
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B49/00—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation
    • B24B49/10—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation involving electrical means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B24—GRINDING; POLISHING
    • B24B—MACHINES, DEVICES, OR PROCESSES FOR GRINDING OR POLISHING; DRESSING OR CONDITIONING OF ABRADING SURFACES; FEEDING OF GRINDING, POLISHING, OR LAPPING AGENTS
    • B24B49/00—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation
    • B24B49/16—Measuring or gauging equipment for controlling the feed movement of the grinding tool or work; Arrangements of indicating or measuring equipment, e.g. for indicating the start of the grinding operation taking regard of the load
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C32/00—Bearings not otherwise provided for
    • F16C32/04—Bearings not otherwise provided for using magnetic or electric supporting means
    • F16C32/0406—Magnetic bearings
    • F16C32/044—Active magnetic bearings
    • F16C32/0444—Details of devices to control the actuation of the electromagnets
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B19/00—Programme-control systems
    • G05B19/02—Programme-control systems electric
    • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
    • G05B19/19—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
    • G05B19/21—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an incremental digital measuring device
    • G05B19/23—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an incremental digital measuring device for point-to-point control
    • G05B19/231—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an incremental digital measuring device for point-to-point control the positional error is used to control continuously the servomotor according to its magnitude
    • G05B19/234—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an incremental digital measuring device for point-to-point control the positional error is used to control continuously the servomotor according to its magnitude with current or torque feedback only
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B19/00—Programme-control systems
    • G05B19/02—Programme-control systems electric
    • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form
    • G05B19/416—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of programme data in numerical form characterised by control of velocity, acceleration or deceleration
    • G05B19/4163—Adaptive control of feed or cutting velocity
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02K—DYNAMO-ELECTRIC MACHINES
    • H02K7/00—Arrangements for handling mechanical energy structurally associated with dynamo-electric machines, e.g. structural association with mechanical driving motors or auxiliary dynamo-electric machines
    • H02K7/08—Structural association with bearings
    • H02K7/09—Structural association with bearings with magnetic bearings
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16C—SHAFTS; FLEXIBLE SHAFTS; ELEMENTS OR CRANKSHAFT MECHANISMS; ROTARY BODIES OTHER THAN GEARING ELEMENTS; BEARINGS
    • F16C2322/00—Apparatus used in shaping articles
    • F16C2322/39—General build up of machine tools, e.g. spindles, slides, actuators
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/37—Measurements
    • G05B2219/37285—Load, current taken by motor
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/45—Nc applications
    • G05B2219/45161—Grinding machine
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
    • G05B2219/00—Program-control systems
    • G05B2219/30—Nc systems
    • G05B2219/49—Nc machine tool, till multiple
    • G05B2219/49271—Air bearing slide, hydraulic, electromagnetic bearing

Definitions

  • the present invention relates to machining apparatus and methods of operating such apparatus.
  • machining conditions are generally determined by the material of the workpiece, the tool being used, and the machining method used.
  • Machining to optimum efficiency is difficult because it is difficult to follow changes of load which are caused by various factors including changes of cutting resistance resulting from changes in the sharpness of a tool. Because of this problem, it is difficult to improve the machining accuracy and machining efficiency.
  • Some machining apparatus have overcome the above-mentioned problem.
  • one machining apparatus is capable of controlling machining by the use of changes of electric power supplied to a spindle driving motor.
  • Another machining apparatus is capable of controlling machining by the use of changes of the bearing pressure during machining.
  • An object of the invention is to overcome such problems and thus improve machining accuracy and machining efficiency.
  • DE-A-2 644 380 describes a machining apparatus comprising a main rotatable spindle having a tool at one end thereof, and supported, in operation, without contact and by magnetic force from radial and axial supporting electromagnets, the energising currents to which are under the control of magnetic bearing control means responsive to outputs from position detecting means for detecting the radial and axial positions of the spindle.
  • a machining apparatus comprising a main rotatable spindle having a tool at one end thereof, and supported, in operation, without contact and by magnetic force from radial and axial supporting electromagnets, the energising currents to the electromagnets being under the control of magnetic bearing control means responsive to outputs from position detecting means for detecting the radial and axial positions of the spindle, and relative movement means to effect relative movement between the tool and a workpiece to be machined, characterised in that there are current measuring means for measuring currents to at least one of the electromagnets, and machining control means for controlling machining conditions according to the measured currents, the machining control means being arranged to control the relative movement means.
  • the machining control means control machining so that electric currents flowing in the electromagnets are maintained according to predetermined conditions in order to produce an optimum machining condition, so that machining can be carried out under optimum machining conditions, for example, cutting load, cutting speed, lifetime of tools, thus improving machining accuracy and machining efficiency.
  • the present invention extends to a method of operating machining apparatus comprising a rotatable spindle having a tool at one end, electromagnets for radially and axially supporting the spindle by magnetic force without contact, and relative movement means to effect relative movement between the tool and a workpiece to be machined, in which method the spindle is rotated, the radial and axial positions of the spindle are detected, and currents are supplied to the electromagnets responsive to such detection, characterised in that the supplied currents are measured and compared with reference values, and the relative movement means is controlled in accordance with the results of such comparisons.
  • a first embodiment of machining apparatus according to the present invention takes the form of a grinding apparatus 1 whose exterior body 2 is generally cylindrical.
  • a spindle 3 is disposed axially within the body 2 and, in operation, is electromagnetically supported by radially disposed electromagnets 5 and 6 at opposite ends of the body 2, so as to float.
  • an electromagnetic motor 8 encircles the spindle 3 and, in operation, rotates the spindle.
  • the spindle 3 has a flange 10 on either side of which are disposed a pair of axially-facing electromagnets 11 and 12 which, in operation, restrict axial displacement of the spindle 3 within the body 2.
  • An electromagnetic radial position sensor 14 (position detecting means) is located in one end cap of the body 2 near the radial electromagnet 5.
  • the position sensor 14 detects separation between the spindle 3 and the internal surface of sensor 14 which corresponds to the internal surface of the radial electromagnet 5 thereby detecting the radial position of the spindle 3 in the vicinity of the electromagnet 5.
  • a similar position sensor 15 is located at the other end of the body for detecting the radial position of the spindle 3 in the vicinity of the electromagnet 6.
  • An electromagnetic axial position sensor 16 is also located in the one end cap of the body 2 for detecting the axial position of the spindle 3 by reference to a step formed between the central region 3 a of the spindle 3 and a smaller diameter end portion 3 b .
  • Protective radial bearings 18 and 19 in end caps of the body 2 surround the smaller diameter portion 3 b of the spindle 3 and a smaller diameter portion 3 c at the other end respectively. These protective bearings 18 and 19 directly support the spindle 3 at the smaller diameter portions 3 b and 3 c , when the power supply to the radial electromagnets 5 and 6 is cut off and consequently they lose the magnetic force to float the spindle 3.
  • a cylindrical grinder 21 is mounted at the tip of the smaller diameter portion 3 b of the spindle 3 so as, in operation, to be rotated by the spindle 3 to grind a workpiece (not shown).
  • the electromagnets 5 and 6 each consist of a set of four electromagnets 5 a to 5 d and 6 a to 6 d .
  • the radial electromagnets are controlled by magnetic bearing control apparatus 20.
  • the diametrally opposite electromagnets 5 a , 5 c and 6 a , 6 c (hereinafter referred to as tangential direction electromagnets), magnetically float the spindle 3 in the neutral position in the vertical plane therebetween, and generate a magnetic force acting against a tangential component force of a machining load acting against the grinder 21.
  • the diametrally opposite electromagnets 5 b , 5 d and 6 b , 6 d (hereinafter referred to as normal direction electromagnets) magnetically float the spindle in the neutral position in the horizontal plane therebetween, and generate a magnetic force acting against a normal component force (in the cutting direction) of the machining load acting against the grinder 21.
  • the workpiece is shifted relative to the spindle 3 for cutting by the rotation of a servo-motor 26 through a ball screw (not shown).
  • Rotation of the servo-motor 26 is measured by a rotary encoder 48, and the position of a servo-motor-driven cutting table (not shown) is determined based on the measured rotation.
  • Signals from the rotary encoder 48 are transmitted through an encoder pulse converter 50 and a position counter 51 to be input into the internal bus 46.
  • the micro-computer 45 operates to store in a RAM store 54, data input from a keyboard 43 into the internal bus 46, changing and erasing data already stored there.
  • the micro-computer 45 includes a CPU 55 which carries out the functions of decoding, operating, and controlling according to a program stored in a ROM store 53, various data input into the internal bus 46 and stored in the ROM store 53 and the RAM store 54. Digital signals output through the internal bus 46 into a D/A converter 56 are converted into analogue or voltage signals therein. These are supplied to a servo-driver 60 which rotates the servo-motor 26 according to the voltage signal, receiving rotational data from the rotary encoder 48, thereby shifting the cutting table by a required amount.
  • Display apparatus 58 comprising a CRT or liquid crystal display, displays information, including commands in response to digital signals input into the display apparatus 58 through the internal bus 46.
  • the grinding apparatus 1 has a workpiece rapidly moved by the cutting table to position A ( Figure 3) adjacent the grinder 21. Then the workpiece is moved between position A and position B, over which range coarse grinding is carried out. Then the workpiece is moved between position A and position C over which range fine grinding is carried out. Finally, the workpiece is withdrawn rapidly from position C in reverse.
  • a constant load is applied to the grinder in normal cutting direction relative to the workpiece.
  • the micro-computer 45 controls the servo-motor 26 so that a constant current always flows in the normal direction electromagnets 5 b , 6 b and 5 d , 6 d . That current is sufficient for coarse grinding.
  • a constant load is applied to the grinder 21 in the normal cutting direction, and the micro-computer 45 controls the servo-motor 26 so that a constant current always flows in the normal direction electromagnets 5b, 6 b and 5 d , 6 d .
  • the micro-computer 45 controls the servo-motor 26 so that the workpiece is withdrawn from the grinder 21 by reverse feed.
  • a START FEEDING instruction ( Figure 5) is given.
  • This starts the servo-motor 26 moving the cutting table.
  • the position of the cutting table is read (P1) by the rotary encoder 48 which passes a signal to the encoder pulse converter 50 ( Figure 4).
  • This is compared in the micro-computer 45 to a reference position, initially position A in this example, and the switch 41 operated so as to contact the A terminal thereof.
  • a signal from the position loop gain according to the difference between the reference position and the current position of the cutting table. This is supplied by the switch 41 to the servo-driver 60 to rotate the servo-motor 26.
  • the present position is repeatedly read and a determination made as to whether it is in the rapid feed range, that is that it has not yet reached the position A. If not, the operation P2 continues to feed the cutting table up to a change point between rapid feed and coarse grinding, that is position A. Thereby, the cutting table is rapidly moved to position A at which coarse grinding is to begin.
  • the determination as to whether the present position is in the rapid feed range becomes negative and a determination is made as to whether the present position is at the grinding completed position, that is position C in this example. If not, a further determination is made as to whether the present position is in the coarse grinding range. If so, operation P4 occurs and a predetermined current value is set during coarse grinding as the reference current value. At the same time, the switch 41 is changed so as to contact the B terminal.
  • the current I flowing in the normal direction electromagnets 5 b , 5 d , 6 b and 6 d is read in operation P6 by the current transformer 29 which supplies the information in signal form to the level converter 31 whence it is taken to be compared to the reference current value.
  • the difference E between the read current value I and the predetermined reference current value is calculated in operation P7.
  • the difference E is then subjected to gain K in operation P8 and passed to the servo-driver 60 as a command to rotate the servo-motor 26 so as to move the cutting table at such a speed as to maintain the measured current value I at the reference current value in operation P9.
  • the currents in the normal direction electromagnets will not be equal to the reference current value if the load on the grinder is more than or less than the desired load.
  • the speed at which the cutting table is moved from the position A to the position 8, that is the coarse grinding range is increased or decreased to maintain the normal direction electromagnet currents equal to the reference value.
  • the present position of the cutting table continues to be read in operation P1. Determinations are made as to whether the present position is in the rapid feed range, at the grinding completed position or in the coarse grinding range. Whilst the former are negative and the latter positive, movement of the cutting table from position A to position B continues. When the position B is reached, the present position is not in the coarse grinding range and a further determination is made as to whether the present position is in the fine grinding range, that is whether it is between positions B and C in this example. If so, then in operation P5 a different predetermined current value is set during fine grinding as the reference current value. This is followed by operations P6, P7, P8 and P9 as before, but with a different reference current to be compared with. This alters the load on the grinder, but again the speed at which the cutting table is moved from position B to position C is increased or decreased to maintain the normal direction electromagnet currents equal to the different reference value during the fine grinding range.
  • the switch 41 changes over to the A terminal and the servo-driver 60 controls the servo-motor 26 to reverse feed the cutting table from the position C until the end of the reversed feed range in operation P3.
  • the servo-motor 26 is controlled in such a manner that each of the loads in the normal direction during coarse grinding range and during fine grinding range becomes constant at a respectively different value, and thereby highly accurate grinding work including improved cylindricality of a workpiece becomes possible.
  • Determinations are made as to whether the present position is either in coarse or fine grinding ranges and, if so, which. If in the coarse grinding range, a predetermined appropriate reference current value is set for comparison with the normal direction electromagnet currents in operation P2. Then when the fine grinding range is reached, a different predetermined reference current value is set for the fine grinding range in operation P3. In either case, in operation P4 the normal direction electromagnet currents are detected by the current transformer 29 ( Figure 6), level converted in the level converter 31 and compared to the current reference current value in a comparator 32. Whilst the detected current is less than the reference current value, the cutting table is fed at constant speed according to whether coarse or fine grinding is called for.
  • the micro-computer 45 determines abrasion of the grinder 21 and outputs a command for correction of the grinder in order to carry out grinding work with optimum cutting efficiency, whereby the grinding work is carried out with high accuracy and high efficiency.
  • a grinding method which includes one step of spark-out is used, in order to improve grinding accuracy.
  • spark-out step grinding is carried out after the fine grinding step whilst the workpiece is not positively fed by the servo-motor.
  • the only relative movement of the workpiece and grinder is due to elastic restoring forces.
  • the purpose of spark-out is to allow completion of grinding with the workpiece and tool relaxed.
  • the time for spark-out is fixed by a timer to be equal for every cycle of grinding work. Because of this, an unnecessarily long time is sometimes spent for spark-out which eventually increases the otherwise shorter time for one cycle of grinding work, thereby resulting in lower efficiency.
  • the third embodiment is used in order to solve this problem.
  • a determination ( Figure 10) additional to those in Figures 5 and 7 is made as to whether the cutting table position is in the spark-out grinding range. If so, the current value I flowing in normal direction electromagnets is read by the current transformer 29, is level converted in level converter 31 ( Figure 9) and compared with a predetermined reference current value. When it is determined that the current value I is less than the predetermined reference current value, and therefore further spark-out grinding is not required, grinding work is completed and the cutting table is reverse fed in operation P2.
  • the predetermined reference current value for spark-out grinding is set in the micro-computer comparator when fine grinding is complete. In this manner, the time for spark-out is made shorter than a time fixed by timer, the grinding work time is shortened, and efficiency is improved.
  • a fourth embodiment of the present invention ( Figures 11 and 12) current values are read not only from normal direction electromagnets 5 b , 5 d , 6 b , 6 d , but also from tangential direction electromagnets 5 a , 5 c , 6 a , 6 c .
  • Abrasion of the grinder 21 is determined based on the ratio of the current value I n of the normal direction, electromagnets and the current value I h of the tangential direction electromagnets, and based on this determination a command for correction of the grinder is output.
  • the position of the cutting table is read in operation P1 ( Figure 12) according to a signal from a rotary encoder 48.
  • a reference current ratio value for coarse grinding is set in operation P2
  • a reference current ratio value for fine grinding is set in operation P3.
  • the current I n flowing in the normal direction electromagnets is read and level converted in operation P4
  • the current value I h flowing in the tangential direction electromagnets is read and level converted in operation P5.
  • the ratio I of the current value I n to the current value I h is calculated in a divider in the micro-computer 45 in operation P6.
  • the ratio I is compared in a comparator with the preset reference current ratio value and if the ratio I is larger than the reference value, it is an indication that the grinder 21 is abraded. Accordingly a command, which requires correction of the grinder to be carried out after the present cycle of grinding work and before the following cycle of grinding work, is input into the display apparatus 58 in operation P7.
  • the above determination method uses the phenomenon that the ratio of the tangential component force and normal component force of the load acting against the spindle changes when abrasion of the grinder 21 develops.
  • the micro-computer 45 determines the abrasion of the grinder 21 and outputs the command for correction of the grinder in order to carry out grinding work with an optimum cutting efficiency, whereby the grinding work is carried out with high accuracy and high efficiency.
  • a workpiece is moved relative to the grinder (or spindle), but the grinder could be moved relative to a workpiece instead.
  • the electromagnets are disposed in a vertically crisscross fashion, but they could be disposed in an obliquely crisscross fashion, in other words in an X fashion instead. In the latter case, current values flowing in all the electromagnets are read, and the tangential and normal components of a load acting against the spindle 3 can be calculated.
  • the machining apparatus having a main spindle supported by magnetic bearings is a grinding apparatus, it can also be used in other machining apparatus such as milling machines, drilling machines and the like.
  • machining control means control to maintain an optimum machining condition based on current values flowing in the electromagnets, whereby machining work is carried out under an optimum condition, and the machining accuracy and efficiency can be improved.
  • the servo-motor is controlled in such a manner that each of machining loads in the normal direction during coarse grinding and fine grinding becomes constant at a respectively different value.
  • the machining control means outputs a command for correction of the grinder on determining abrasion of the grinder, whereby a workpiece is always ground with an optimum cutting efficiency, and therefore highly accurate and highly efficient grinding work can be achieved.
  • the time for spark-out can be made shorter than a time duration set by timer, which shortens the total grinding time and improves grinding efficiency.
  • the workpiece moves towards and away from the rotating tool or grinder 21 in a direction normal to the axis so that current is supplied to the normal direction electromagnets to resist any tendency of the spindle 3 to move under the cutting load. If the workpiece is moved in some other direction relative to the tool or grinder, then currents are supplied to all the electromagnets to counteract the cutting load. If the relative movement is in the axial direction, then the currents to the axial electromagnets are controlled to resist any consequent axial movement of the spindle relative to the body 2. In all cases, the currents supplied to the elecromagnets may be used to control the relative speed of the workpiece to the tool or grinder, and thus to adjust the cutting load to the optimum for the particular operation.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Manufacturing & Machinery (AREA)
  • Human Computer Interaction (AREA)
  • Automation & Control Theory (AREA)
  • Electromagnetism (AREA)
  • Power Engineering (AREA)
  • Fluid Mechanics (AREA)
  • Automatic Control Of Machine Tools (AREA)
  • Turning (AREA)
  • Constituent Portions Of Griding Lathes, Driving, Sensing And Control (AREA)
  • Magnetic Bearings And Hydrostatic Bearings (AREA)

Claims (7)

  1. Bearbeitungseinrichtung umfassend eine drehbare Hauptspindel (3) mit einem Werkzeug (21) an einem ihrer Enden, welche im Betrieb ohne Kontakt und durch die magnetische Kraft von radial und axial tragenden Elektromagneten (5, 6, 11, 12) getragen ist, wobei die Erregerströme für die Elektromagneten unter der Steuerung von magnetischen Lagersteuermitteln (20) stehen, welche auf Ausgaben von Stellungserfassungsmitteln (14, 15, 16) zum Erfassen der radialen und axialen Stellungen der Spindel (3) ansprechen, sowie Relativbewegungsmittel (26) um eine relative Bewegung zwischen dem Werkzeug (21) und einem zu bearbeitenden Werkstück zu bewirken, dadurch gekennzeichnet, daß Strom-Meßmittel (28, 29) zum Messen der Ströme zu wenigstens einem der Elektromagneten vorgesehen sind, sowie Bearbeitungssteuermittel (45) zum Steuern der Bearbeitungsbedingungen gemäß den gemessenen Strömen, wobei die Bearbeitungssteuermittel (45) dazu eingerichtet sind, die Relativbewegungsmittel (26) zu steuern.
  2. Einrichtung nach Anspruch 1, in welcher das Bearbeitungssteuermittel (45) die Relativbewegung zwischen dem Werkzeug (21) und einem Werkstück in Antwort auf die gemessenen Ströme steuert, um eine voreingestellte Schnittbelastung beizubehalten.
  3. Einrichtung nach Anspruch 1 oder 2, in welcher das Bearbeitungssteuermittel (45) die Schnittgeschwindigkeit zwischen dem Werkzeug (21) und dem Werkstück in Antwort auf die gemessenen Ströme steuert.
  4. Einrichtung nach einem der vorhergehenden Ansprüche, umfassend Mittel (26, 48, 50, 51) zum Anzeigen der relativen Stellungen des Werkzeugs (21) und des Werkstücks, wobei das Bearbeitungssteuermittel (45) auf derartige Anzeigen anspricht, um Referenzstromwerte zu setzen, mit welchen die gemessenen Ströme verglichen werden.
  5. Einrichtung nach Anspruch 4, in welcher das Bearbeitungssteuermittel (45) auf eine Anzeige, daß die relativen Stellungen des Werkzeugs (21) und des Werkstücks derart sind, daß das Ende der Bearbeitung erreicht ist, anspricht, um das Werkstück von dem Werkzeug (21) wegzubewegen.
  6. Einrichtung nach Anspruch 4, in welcher das Bearbeitungssteuermittel (45) auf eine Anzeige, daß die relativen Stellungen des Werkzeugs (21) und des Werkstücks derart sind, daß das Ende der Bearbeitung erreicht ist, anspricht, um das Wegbewegen des Werkstücks von dem Werkzeug (21) zu verzögern, bis die gemessenen Ströme niederer sind als der voreingestellte Bezugswert (Ausfunken).
  7. Verfahren zum Betätigen einer Bearbeitungseinrichtung umfassend eine drehbare Spindel (3) mit einem Werkzeug (21) an einem Ende, Elektromagneten (5, 6, 11, 12) zum radialen und axialen Tragen der Spindel durch magnetische Kraft ohne Kontakt, und Relativbewegungsmittel (26) um eine relative Bewegung zwischen dem Werkzeug (21) und einem zu bearbeitenden Werkstück zu bewirken, in welchem Verfahren die Spindel rotiert wird, die radialen und axialen Stellungen der Spindel erfaßt werden und in Antwort auf eine derartige Erfassung den Elektromagneten Ströme zugeführt werden, dadurch gekennzeichnet, daß die zugeführten Ströme gemessen und mit Referenzwerten verglichen werden, und die Relativbewegungsmittel (26) gemäß den Ergebnissen derartiger Vergleiche gesteuert werden.
EP88310398A 1987-11-06 1988-11-04 Vorrichtung und Verfahren zur spanabhebenden Bearbeitung Expired - Lifetime EP0315469B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP280516/87 1987-11-06
JP62280516A JP2516382B2 (ja) 1987-11-06 1987-11-06 磁気軸受を主軸にもつ加工装置

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EP0315469A2 EP0315469A2 (de) 1989-05-10
EP0315469A3 EP0315469A3 (en) 1990-08-22
EP0315469B1 true EP0315469B1 (de) 1993-03-03

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EP (1) EP0315469B1 (de)
JP (1) JP2516382B2 (de)
KR (1) KR970003147B1 (de)
DE (1) DE3878832T2 (de)

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Publication number Publication date
EP0315469A2 (de) 1989-05-10
KR890007845A (ko) 1989-07-06
US5027280A (en) 1991-06-25
KR970003147B1 (ko) 1997-03-14
DE3878832D1 (de) 1993-04-08
DE3878832T2 (de) 1993-06-09
JPH01127254A (ja) 1989-05-19
JP2516382B2 (ja) 1996-07-24
EP0315469A3 (en) 1990-08-22

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